1. Field of the Invention
The present invention relates to a motor driving integrated circuit.
2. Description of the Related Art
Motor driving integrated circuits are included in various electronic apparatuses provided with a motor and, together with the motor, are considered to be important parts. Therefore, recently, in order to respond to various demands such as higher efficiency, lower power consumption, and enhanced usability, a plurality of functions are included in a motor driving integrated circuit of one-chip (see, e.g., Japanese Patent Application Laid-Open Publication No. 2001-320890).
For example, a PWM driving system is adopted for the higher efficiency. The PWM driving system is a system for controlling the number of rotation of the motor by adjusting on-duty (=on-time/(on-time+off-time)) of a driving transistor. The driving transistor has an advantage of reducing power consumption since the driving transistor is not always in the on-time but is in repeated cycles of the on-time and the off-time when energizing a drive coil. The on-duty is adjusted by slicing a triangular-wave signal with a level of a speed control voltage corresponding in level to the on-duty and being applied from an external microcomputer, etc., by way of a speed control input terminal so as to generate a PWM signal, and applying the PWM signal to a control electrode (base electrode or gate electrode) of the driving transistor.
A power off function is adopted for reducing the power consumption. The power off function is a function of shutting off power supply to circuits of the motor driving integrated circuit when rotation driving of the motor is stopped and the control in the motor driving integrated circuit is not performed for a predetermined period. Specifically, it is a function of turning off a power supply circuit and a bias circuit in the motor driving integrated circuit based on a power off signal input from the external microcomputer, etc., by way of a power off terminal.
Furthermore, a start/stop function is adopted for enhancing usability. The start/stop function is a function of controlling start or stop of the rotation driving of the motor at appropriate timing. Specifically, it is a function of starting the rotation driving of the motor at one level and stopping the rotation driving of the motor at the other level, out of binary level of a start/stop signal input from the external microcomputers, etc., by way of a start/stop input terminal.
To respond to a variety of demands, the motor driving integrated circuit is provided with a plurality of separate terminals, such as the speed control input terminal, the power off terminal, and the start/stop input terminal. However, in accordance with the incorporation of a plurality of the functions into the motor driving integrated circuit of one-chip as above, there arises a new problem of an increase in size of the circuit due to an increase in number of terminals.